In the present day, various types of processing apparatus are employed to treat or process substrates with ions. For processing substrates such as semiconductor substrates, ions may be used to etch layers or features on a substrate. Ions may also be used to deposit a layer or structures on a substrate, to implant a species into a substrate, or to amorphize a substrate. Techniques have also been developed to monitor processing of a substrate in order to control the processing of a substrate. In the present day, ion implantation tools provide increasing versatility for implantation of a substrate or wafer. While previous development focused on improving the uniformity of wafer processing, many present-day customers of ion implantation apparatus may request various patterns of non-uniform process control for Precision Materials Engineering (PME). In some methods of implantation an ion beam may be provided as a spot beam whose cross-sectional area is smaller than the area of a substrate to be implanted. The spot beam may be scanned along a first direction while the substrate is moved along a second direction, for example, a direction perpendicular to the first direction. In particular methods, non-uniform implantation may be performed by scanning a spot beam according to a predetermined waveform in order to provide variable ion doses to different regions of a substrate.
In order to provide accurate dose control for ion implantation of a substrate using a scanned spot beam, current monitors may be provided at or near a substrate, such as Faraday cup monitors. In some ion implanters, real-time monitoring of a scanned spot beam is performed to estimate ion dose provided to a substrate. A current sensor such as a Faraday cup may be provided adjacent to a substrate to intercept a spot beam scanned back and forth along a first direction while a substrate is scanned in a perpendicular direction. The real-time monitoring may be used to adjust the scanning of a spot beam when the measured ion dose at the current sensor does not match a target ion dose, for example.
In the case of targeted non-uniform ion implantation, a waveform may be applied to the different scans to vary scan rate of the spot beam as the spot beam scans across a substrate. The variation of scan rate across different portions of a substrate has the effect of changing the integrated ion dose implanted into the substrate at different locations along the scan direction. When the variation of scan rate is repeated over multiple spot beam scans as the substrate is moved in a perpendicular direction, a two-dimensional pattern of implantation may be generated where different regions of a substrate receive different ion doses.
A limitation of the aforementioned targeted non-uniform ion implantation lies in the ability to control non-uniform implantation when the spot beam exceeds a certain size. In some cases the size of a spot beam may cause the spot beam to overlap at the same time a current monitor and a substrate region to be implanted. This overlap may limit the ability to apply a targeted waveform to the substrate to generate a targeted non-uniform implantation and at the same time accurately measure ion dose provided to the substrate.
With respect to these and other considerations the present improvements may have been needed.